My house has been fitted with water traps in toilet and bathrooms drains which is quite good, but I can see that my kitchen sink, washing machine outlet pipe and regular wash basin don't have water traps.
Shouldn't we have water traps to avoid gas or cockroach from entering the building through drainage?
My plumber argued that keeping the extra water traps in kitchen sink and other places will have dirty water and this can be smelly but I'm not buying his argument.
Additional info: The town that I'm living in doesn't have integrated sewer or grey water collection system.
It's just that I have six dry wells for grey water collection around my home. All 6 dry wells have a 1 foot high air vent. I'm just worried that toxic gas or mosquito or cockroach or some other rodents might enter through the plumbing line.